Process for the manufacture of rustless iron



United States Patent PRocnss non THE MANUFACTURE OF RUSTLESS IRON SampeiKatakura, 60-5 Gotanda, Shinagawa-ku, and Kenkichi Tachiki, 117 SauyawhoMeguro-ku, both of Tokyo, Japan No Drawing. Filed Dec. 24, 1958, Ser.No. 782,621

1 Claim. (CI. 75-28) The present invention relates to a process forproducing rust resistant iron by treating iron powder in contact withmetallic calcium powder, with its object being to provide a novel methodfor obtaining stainless iron economically and simply.

Iron, like other metals in general tends to increase in resistance torusting or corrosion with increase of the purity of the metal. Eventhough no perfect removal of impurities is attained, a sutficientcorrosion resistance may be obtained depending upon the treatment.

We have found, in accordance with the invention, that impurities in ironcan be removed therefrom, as shown in Table 1, by bringing pulverizediron into contact with powdered metallic calcium in an atmosphere ofargon or other inert gases and that the resistance of the iron tocorrosion is thus increased as described hereinafter.

In the above-mentioned test, as shown in Table 1, ferrous substancescontaining impurities, A, B, C of 250- 300 mesh are brought into contactwith metallic calcium powder at 30 C. for 12 to 24 hours, with stirringevery two hours, and thereafter the iron ingredient is separated fromcalcium by elutriation, such iron ingredients being shown in Table 1 asmaterials after treatment.

The respective results of those materials being either exposed in air orimpregnated in 30% (by weight) sulfuric acid solution is as shown inTable 2.

TABLE 2 Rust proof test (a) Rusting in air:

after 1 after 6 month months H0118 u IlOIlG.

110119- X10116. 110116--.. none.

(b) impregnation test (temperature: 20 C.) in sulfuric acid solution (30by weight percent):

Corrosion loss (g./cm. /hr.)

As shown in the above table, the removal of impurities from iron bycalcium treatment is not always perfect, but the corrosion resistanceshows a similar result as in a stainless steel. It is presumed that notonly the surface but also to a considerable depth the iron particleshave been converted into a peculiar state by calcium.

The iron powder used in this invention ranges from common steel, Swedishsteel, reduced iron and further to carbonyl iron. Difiiculty or easinessof the reaction is dependent on the respective iron material. Forinstance, the reaction is easier in common steel than in Swedish steel.As the reaction with calcium is a reaction between solids, the powder ispreferable in a fine state. Turnings of the above-mentioned ironmaterial is pulverized in a pulverizing apparatus such as an edge millto a fine powder of about 250 mesh, which is a suitable size for thispurpose. On the hand, as to metallic calcium, those obtained by areducing process or an electrolytic process are used, which arepulverized in 200 mesh powder in a cyclone crusher for use. In thefollowing is shown an example of analyses of calcium by a reductionmethod.

Fe Al Mg Si Ga Approx. 20 to 30 parts thereof are added to parts of theabove mentioned iron. The contact treatment of the iron powder with thecalcium powder is carried out in an atmosphere of inert gas, such asargon, etc. In practice, stirring is made from time to time in order tobring about good contact of both materials.-

This treatment is generally carried out at ordinary temperatures. Inparticular, heating is effected to some extent, when reaction occurs asin the case of Swedish steel.

The duration of treatment requires ordinarily 24 hours depending uponthe grain size and contamination degree, etc. of the raw powderedmaterial. The treatment is continued until the colour of the metalpowder mixture under treatment changes to brown colour; In order toseparate the iron powder treated, the elutriation method is convenient,since the iron powder is heavier and has become inactive to water'whilethe calcium used is relatively light. The iron powder thus obtained isextremely strong after being dried by removing water. It is moreoverhighly durable and lustrous as well as remarkably resistant to corrosionas mentioned above.

The rust resistant iron powder thus obtained is suitable for use inordinary powder metallurgy. Moreover, when said stainless iron ismoulded, sintered in an inert gas atmosphere and forged, it becomessomething similar to stainless steel. Besides, a solid stainless ironmaterial can be obtained having under-mentioned characteristicproperties and can be fabricated for several purposes.

EXAMPLE 1 from by the elutriation process. The separated ironpowderislustrous and will not lose luster even if it is exposed in airfor an extended period of time.

If this iron powder is to be used, for example in making lamps, theabove-mentioned iron powder is dried and formed in a moulding machine,under'a pressure of 3 ton/cm. The moulded product is sintered in acrucible. The sintering is carried out in an argon atmosphere in a highfrequency induction furnace. Sintering is effected in a time ratio of 3hours to kg. raw material. This sintered material is forged during itscourse of cooling after sintering. Thus manufactured lamp shaped rustresistant iron is remarkably corrosion resistant and has variousmechanical features.

EXALIPLE 2 10 kg. of turnings of Swedish steel containing less than 0.1%carbon are pulverized in an edge mill to 250 to 300 meshes, which areput in an iron receptacle electroplated withplatinum. In argon gasatmosphere, 3 kg. of powdered calcium similar to that described inExample 1 are added to the iron powder and thoroughly mixed and allowedto stand for 24 hours. In this case, the mixture is slightly heated atto 30 C. above room temperature, and mixed again every two hours duringreaction. The calcium which absorbed impurities is separated byelutriation after the reaction has been finished. The thus treatedmaterial is lustrous as that obtained in the said embodiment 1) and,further, its corrosion resistance is excellent.

EXAMPLE 3 10 kg. reduced iron powder of around 0.05% C are furthercrushed in an edge mill to 250to 300 meshes, and 25 kg. metallicvcalcium similar to that described in Example 1 are added to the materialin an argon gas atmosphere. This mixture is allowed to stand at roomtemperatures for 18 hours, during which time it is stirred again everytwo hours. The iron particles having completed the reaction areseparated perfectly from the cal-. cium having absorbed impurities, bythe elutriation proc- 4 ess. The thus treated material is lustrous,similarly as that obtained in the above-mentioned Example 2. Itscorrosion resistance, further, is good.

EXAMPLE '4:

2 kg. metallic calcium like that used in Example 3 pulverized to 200mesh are added to 10 kg. carbonyl iron powder in argon gas atmosphereand mixed thoroughly and let stand for twelve hours at roomtemperatures, during which time it is stirred again every twohours. Theiron particles having completed the reaction are separated perfectlyfrom the calcium having absorbed impurities by the elutriation process.The thus treated material is extremely lustrous, similarly as thatobtained in the above-mentioned example, and has high purity. Itscorrosion resistance is extremely high.

What we claim:

The process for the production of rust resistant iron which comprisesmixing parts finely divided iron containing metallic impurities with 20to 30 parts powdered metallic calcium in an inert gaseous atmosphere toform amass wherein the calcium and iron particles are in intimatecontact, maintaining the particles in intimate contact for from 12 to 24hours at a temperature in the range of 20 to 3 0'C. above roomtemperature with stirring every two hours until the mass takes on abrown coloration, and separating the iron particles from the mass.

References Cited in the file of this patent UNITED STATES PATENTSRostron Mar. 27, 1951 OTHER REFERENCES Jones: Powder Metallurgy, EdwardArnold & Co., London, 1943, page 49.

Goetzel: Treating of Powder Metallurgy, volume II, 1950, IntersciencePublishers, Inc., New York, page 627.

